1. Field of the Invention
This invention relates to a method of protecting eyes from welding rays in arc welding and an apparatus therefor, and more particularly to such eye-protecting method and apparatus which are adapted to utilize a light-intercepting mask or personal eye-protector for welding having a filter plate formed of a material exhibiting an electro-optic effect arranged thereon.
2. Description of the Prior Art
Conventionally, a personal eye-protector or light-intercepting mask for welding has been widely used to prevent welding rays from entering the eyes of an operator in arc welding. The conventional personal eye-protector often includes a light-intercepting filter plate formed of an electro-optic material. The personal eye-protector of such a type is adapted to keep the filter plate light-permeable to form a bright field until a welding electrode mounted on an electrode holder is contacted with the portion of works to be subjected to welding to generate arc welding rays, and detect the arc welding rays to cause the filter plate to extinguish the welding rays passing therethrough to form a dark field after the welding rays are generated. Such actuation of the filter plate is controlled in a manner such that a light receptor detects arc welding rays to generate a detection signal, which carries out the on-off control of a voltage applied to the filter plate formed of a material exhibiting an electro-optic effect such as, for example, (Pa, La)(Zr, Ti)O which is an optically transparent electro-optic ceramic material (hereinafter referred to as "PLZT"), liquid crystal or the like.
Such a material as PLZT or the like indeed effectively intercepts arc welding rays; however, it causes a response delay which corresponds the sum of response time of an element level and response time of a circuit system over a period from the on-off control of the voltage to the exhibition of function as an optical shutter, during which it fails to intercept arc welding rays and therefore prevent arc welding rays from entering eyes of an operator.
In arc welding operation, as shown in FIG. 1, arc welding rays are generated with rapid rising, resulting in the conventional personal eye-protector or light-intercepting mask constructed as described above failing to prevent a large amount of arc rays from entering the eyes of an operator. More particularly, unfortunately, a light receptor is not adapted to detect arc welding rays at the same time of the generation. Instead, it is adapted to start the actuation when arc welding rays reach a threshold level q.sub.1 to generate an output signal. This is for the purpose of blocking noise due to the sunlight or illumination. Accordingly, arc welding rays increase in amount to a level indicated by q.sub.2 in FIG. 1 when it comes time (t.sub.1) for the filter plate to close, resulting in substantially all the rays generated by the time passing through the filter plate without being extinguished.
This causes an operator to suffer from electric ophthalmia due to inflammation on the horny coat or conjunctiva of an eye, because arc welding rays contain a large amount of ultraviolet rays. Further, this causes eye trouble such as muddiness of the crystalline lens or the like due to the exposure to infrared rays contained in arc welding rays for a long period of time.